Membrane Pore Size Research Articles

Optimizing Nanobubble Production in Ceramic Membranes: Effects of Pore Size, Surface Hydrophobicity, and Flow Conditions on Bubble Characteristics and Oxygenation.

Precise control of nanobubble size is essential for optimizing the efficiency and performance of nanobubble applications across diverse fields, such as agriculture, water treatment, and medicine. Producing fine bubbles, including nanobubbles, is commonly achieved by purging gas through porous media, such as ceramic or polymer membranes. Many operational factors and membrane properties can significantly influence nanobubble production and characteristics. This study examines how membrane pore size, surface hydrophobicity, and gas/water flow conditions affect nanobubble size and concentration. Findings reveal that reducing the ceramic membrane pore size from 200 to 10 nm slightly decreased the mean nanobubble diameter from 115 to 89 nm. Furthermore, membranes with a hydrophilic outer surface and hydrophobic pore surface generated smaller nanobubbles with higher concentrations in water. Additionally, a high water cross-flow rate (e.g., >1 L·min-1) increased the nanobubble concentration, though bubble size remained unaffected. In contrast, the gas flow rate had a more pronounced effect. Increasing the gas flow rate from 0.5 to 12 L·min-1 significantly raised the nanobubble concentration from 3.09 × 108 to 1.24 × 109 bubbles·mL-1 while reducing the mean bubble diameter from 100 to 79 nm. An interfacial force model was applied to analyze bubble detachment at the membrane pore outlet, considering factors such as gas flow/pressure, surface tension, and shear forces from the water flow. These findings offer valuable insights into the mechanisms governing nanobubble generation via gas injection through porous membranes.

Synthesis of UiO-66-NH2@PSF Hollow Fiber Membrane with Enhanced Simultaneous Adsorption of Pb2+ and Phosphate for Hydrogen Peroxide Purification.

Electronic grade hydrogen peroxide plays a crucial role in the fabrication of large-scale integrated circuits. However, hydrogen peroxide prepared by the anthraquinone method contains impurities such as lead ions (Pb2+) and phosphate, which can seriously affect the yield of the circuit. Traditional adsorbent materials have difficulty in solving the problem of simultaneous adsorption of trace anions and cations in hydrogen peroxide due to the single adsorption site and poor adsorption kinetics. In this study, UiO-66-NH2 was prepared by introducing a -NH2 group on the terephthalic acid ligand, and a series of hybrid matrix hollow fiber membranes with different UiO-66-NH2 contents were prepared by loading it on polysulfone (PSF). This initiative not only improved the pore size and water flux of hollow fiber membranes but also enhanced the removal efficiency of ions from hydrogen peroxide solution, thereby facilitating practical application. Among them, UiO-66-NH2@PSF-1.5 showed the best adsorption of phosphate and lead ions with adsorption capacities of 3.099 and 2.160 mg g-1 and reached the removal efficiency of 67.1 and 60.1%, which fully confirms the practicability in the purification of electronic chemicals. This work innovatively proposes that UiO-66-NH2@PSF hybrid matrix hollow fiber membranes have great potential as simultaneous adsorbents for cations and anions in the efficient purification of electronic grade solvents.

The Effects of Microseconds Electroporation on Pore Size, Viability and Mitochondrial Membrane Potential of Cervical Cancer Cells

The Effects of Microseconds Electroporation on Pore Size, Viability and Mitochondrial Membrane Potential of Cervical Cancer Cells

Pulsatile Ion Transport in Nanofiltration Membranes Coupled with Electrically Tunable Pore and Hydroxyl Electrostatic Interactions.

Pulsatile ion transport facilitates the adjusted transfer of substances, meeting the requirements for the gradient and timed separation of multiple components in membrane processes. Responsive nanofiltration membranes are thus currently receiving widespread attention but face limitations due to their narrow performance adjustment range. Herein, hydroxyl functional groups were introduced into electrically responsive nanofiltration membranes to broaden the adjustment range of separation performance through a combination of pore size sieving and functional group interactions, resulting in a greater change in rejection and flux compared to the original membrane. Membrane pore size is regulated by polypyrrole volume changes and becomes more variable when the cation's hydration radius is smaller. Although the hydroxyl group did not affect the charge transfer or volume change capacity of polypyrrole, it enhanced ion-pore interactions during ion transport, which was particularly pronounced in smaller nanochannels. The size effect of functional group interactions more strongly enhances the transmembrane energy barrier in the reduced state compared with the oxidized state, ultimately resulting in greater modulation of performance. This coupling strategy provides insights into the design of responsive membranes, offering the potential to achieve gradient separation of various solutes.

Atomically distributed Al-F3 nanoparticles towards precisely modulating pore size of carbon membranes for gas separation

To confront the energy consumption, high performance membrane materials are urgently needed. Carbon molecular sieve (CMS) membranes exhibit superior capability in separating gas mixtures efficiently. However, it remains a grand challenge to precisely tune the pore size and distribution of CMS membranes to further improve their molecular sieving properties. Herein, we report an approach of finely modulating CMS pore structure by using the reactive Al(CH3)3 to in situ defluorinate the polymer precursor to form Al-Fx(CH3)3-x in the polymer matrix, which is further converted to atomic-level Al2O3 and Al-F3 in the polymer matrix. These nanoparticles play the key role in regulating the pore size of CMS membranes by suppressing the formation of unfavorable large pores during pyrolysis, thus enhancing the gas selectivity considerably. The resultant CMS membranes demonstrate a H2/CH4 and CO2/CH4 selectivity of 192.6, and 58.4, respectively, 128% and 93% higher than the untreated samples, residing far above the latest upper bounds.

Purification of mesenchymal stromal cell-derived small extracellular vesicles using ultrafiltration.

Mesenchymal stromal cell-derived small extracellular vesicles (MSC-sEVs) are pivotal for the curative effects of mesenchymal stromal cells, but their translation into clinical products is hindered by the technical challenges of scaled production and purification. Ultrafiltration, a pressure-driven membrane separation method, is well known as an efficient, scalable, and cost-effective approach for bioseparation. However, there has been little study so far that comprehensively evaluates the potential application of ultrafiltration for scaled sEV isolation and purification. In this study, the feasibility and effectiveness of ultrafiltration for MSC-sEV isolation and purification are studied, and the effects of key process design and operational parameters, including the membrane pore size, transmembrane pressure (TMP), stirring speed (shear rate), feed concentration, are quantified using a stirred cell setup. Results revealed that 500kDa molecular weight cut-off (MWCO) polyethersulfone membrane demonstrated superior suitability for MSC-sEV separation, yielding higher purity and productivity compared to 100 and 300kDa MWCO membranes of the same material. The MSC-sEV productivity and purity could also be improved by applying a moderate stirring speed and lower operational pressure, respectively. Isovolumetric diafiltration was incorporated to enhance the purity of MSC-sEVs, successfully removing about 99% of protein contaminants by six diafiltration volumes (DVs). Subsequently, a fed-batch ultra-diafiltration (UF/DF) process with optimised filtration parameters was developed and compared with the currently most used ultracentrifugation (UC) method, showing exceptional effectiveness and performance in the isolation of MSC-sEVs: it increased the recovery of MSC-sEV from 20.59% to 60.88% (about three folds increase) and nearly doubled the purity, while also reducing processing time from over 4h to 3.5h, with a potential further reduction to less than 2.5h through automation. The study concludes that ultrafiltration could be a promising method for both lab-scale preparation and industrial-scale manufacture of MSC-sEVs, offering advantages of high recovery, scalability, fast, and cost-effectiveness.

Molecular Design of Positively Charged 3D Covalent-Organic Framework Membranes for Li+/Mg2+ Separation.

3D covalent-organic framework (3D COF) membranes have unique features such as smaller pore sizes and more interconnected networks compared with 2D COF counterparts. However, the complicated and unmanageable fabrication hinders their rapid development. Molecular simulation, which can efficiently explore the structure-performance relationship of membranes, holds great promise in accelerating the development of 3D COF membranes. In this study, a series of 3D-COF membranes (TFPM-Pa-X) is designed with different charge densities (fully charged, partially charged, and neutral) and interpenetration numbers (2-, 3-, 4-, and 5-fold), subsequently investigate their contributions to Li+/Mg2+ separation through molecular simulation. Membrane morphology and pore size are found to strongly depend on the charged density and interpenetration number. The pore size and Cl- ion density play a crucial role in governing membrane separation performance. TFPM-Pa-X membrane with a smaller interpenetration number and a higher charge density promotes Li+/Mg2+ separation. The fully charged 2-fold interpenetrated membrane has superior performance in breaking the trade-off between the flux of Li+ (JLi +) and the selectivity of Li+ over Mg2+ (SLi + /Mg 2+). This study may facilitate the rational design of new 3D COF membranes for high-performance ion separation.

Application of Membrane Filtration for Microalgae Harvesting and Protein Separation

The seek for sustainable protein sources has led to the exploration of microalgae as an alternative. Membrane filtration, known for its environmental friendliness, holds promise for purifying protein from microalgae. This research focuses on the protein purification from Chlorella vulgaris microalgae using polyethersulfone (PES) membrane. This research aims to investigate the effect of membrane composition for enhanced microalgae harvesting and protein purification, as well as evaluating the effects of membrane pore sizes and porosity on the performance. Three membrane compositions were evaluated, which are 18% PES, 15% PES, and 12% PES. The membranes were tested for efficiency in microalgae harvesting and protein filtration through dead-end filtration. SEM analysis, contact angle analysis, and theoretical calculations were used to assess membrane characteristics. In terms of algae harvesting, both 18% PES and 15% PES were better than 12% PES in terms of retention of algae. Lowest protein rejection or high protein recovery in the permeate was achieved using 18% PES while 12% PES gave the highest rejection or low protein recovery. Our result can provide valuable guidance for optimizing PES membrane compositions to enhance microalgae-based processes.

Construction of Photothermal Intelligent Membranes for Point-of-Use Water Treatment.

For the removal of waterborne pathogens in remote areas and disaster emergency situations, point-source water treatment methods are more suitable. Photothermal sterilization is ideal for point-of-use (POU) systems, as it effectively eliminates pathogens without secondary pollution or bacterial resistance issues. By combining photothermal with membrane treatment, these membranes rapidly heat up under near-infrared (NIR) light, enabling both bacterial retention and sterilization. However, the decrease in membrane flux due to pore clogging during water treatment can significantly impact membrane efficiency. And adjusting the membrane pore size can significantly enhance flux recovery during cleaning, thereby restoring membrane efficiency. By synthesis multifunctional membranes that combine bacteria retention, sterilization, and flux recovery, it can meet the requirements of point-source water treatment: compact size, high efficiency, good safety, and easy maintenance. In this study, we developed an intelligent thermally responsive membrane (NIPAN@CNTs/PAN) by incorporating carbon nanotubes (CNTs) and forming a copolymer of N-isopropylacrylamide and polyacrylonitrile (NIPAN) coating into polyacrylonitrile membranes, offering dual functions of photothermal sterilization and self-cleaning. With 3% CNTs, the membrane achieves 100% sterilization within 6 min of NIR exposure, while the NIPAN layer's added roughness boosts photothermal efficiency, achieving 100% sterilization within 4 min. Rinsing at 50 °C improved flux recovery from 50% to 87% and reduced irreversible fouling from 49.7% to 12.9%, demonstrating stable performance over multiple cycles and highlighting its potential for long-term use in practical POU applications.

Removal of pharmaceutical compounds from sewage effluent by the nanofiltration membrane

Membrane is a promising technology for water treatment, and its commercial production has emerged globally. However, commercial membranes' effectiveness is still uncertain due to the new types of contaminants, such as pharmaceutical compounds (PC). Thus, in the current work, the performance of two commercial membranes (NFX and GC) has been evaluated using feed water from the effluent of sewage treatment plants (STP) and hospital wastewater (HWW). The spiked feed water contains PC classes of analgesics/anti-inflammatory, anti-hypertensives, beta-blockers, and psychiatric/antidepressants. The percentage difference between feed and permeate was measured. While the fouling properties of the membranes are also evaluated using STP and HWW as feed, along with the pure water flux in a variable-pressure setting, the results showed that NFX exhibits excellent, consistent rejection for the targeted PCs (>80 %). GC showed a broader range of rejection (10 % to 90 %) and presented a better flux flow than NFX. The main rejection factor is due to the membrane's pore size variation and the layer construction, which refer to the absorption, size exclusion, and diffusion of the PCs instead of the type of feed water and the flux. Current work provides scientific data on the diverse fabrication and market-available types of membranes, which would pose various efficiencies towards the type of targeted pollution.

Development of an in vitro three-layered skin wound healing model for pre-clinical testing

Abstract Skin wound healing involves many cell types in a stepwise process of tissue regeneration. Reepithelialization is an essential characteristic of successful healing. In tissue engineering, mimicking the complex process of injury repair in vitro is challenging and requires the development of advanced skin models. In this study, a simple and reproducible method for wounding three-layered skin models on membranes with different pore sizes (0.4, 1, 3 μm) was established. The model allows the investigation of reepithelialization processes in a more complex environment. Hemalaun-eosin (HE) and 3-[4,5-dimethylthiazole-2-yl]-2,5- diphenyltetrazolium bromide (MTT) staining proved sufficient removal of the epidermis directly after wounding. An increasing pore size of the culture membrane delayed the reepithelialization time. Transepithelial electrical resistance (TEER) measurements provided non-invasive monitoring of reepithelialization, showing increasing values 4 days after wounding for the skin models on 0.4 and 1 μm membranes but not for those on 3 μm membranes. Cytokine quantification of interleukin (IL)-6 and IL-8 complemented the TEER results with increasing levels directly after wounding for all skin models. This skin wounding model could be used to simulate different wounding scenarios and test wound matrix materials. Furthermore, it could be adapted by adding immune cells to resemble the in vivo setup more closely.

Post-docking hydrophilic Ag-MOF-303 filled in TFC for nanofiltration of charged PhACs in water

Modifying membrane pore size and surface charge to enhance nanofiltration selectivity presents a crucial challenge in managing pollutants with varying charge properties. This study introduces Ag-MOF-303, synthesized by incorporating Ag into hydrophilic MOF-303 through molecular docking, effectively reducing the pore size to the nanofiltration scale. Subsequently, Ag-MOF-303 was deposited onto a PVDF substrate via interfacial polymerization, forming thin-film composite (TFC) polyamide membranes with enhanced selectivity and permeability. Notably, Ag-MOF-303@PVDF is positively charged, enabling the removal of differently charged pollutants from water. Structure-activity analysis confirmed the effective construction of the functional layer, where the Al3+ and Ag+ content significantly influenced the membrane’s charge properties. Cross-flow filtration experiments revealed a permeability of 14 L·m−2·h−1·bar−1 for Ag-MOF-3030.2%@PVDF, achieving rejection rates exceeding 90 % for CaCl2 and MgSO4 due to the Donnan effect. The membrane showed notable selective removal of six pharmaceutically active compounds with varying charges, maintaining a selectivity coefficient around 70, driven by the combined effects of Donnan exclusion and size sieving. Moreover, Ag-MOF-3030.2%@PVDF displayed stable pore size at 0.4 nm, achieving over 80 % flux recovery after protein and lysozyme fouling, thereby enhancing antifouling and antibacterial properties. This novel strategy of utilizing hydrophilic MOF-303, modified via molecular docking to reduce pore size for the nanofiltration of variously charged micropollutants, provides valuable insights into MOF post-modification techniques and the separation mechanisms in nanofiltration, thereby expanding the application potential of positively charged nanofiltration membranes.

Pore-scale study of liquid water transport in gas diffusion layers with in-plane non-uniform distributed pore size of polymer electrolyte membrane fuel cell

Timely removal of liquid water and the supply of the reaction gas in the gas diffusion layer (GDL) plays a critical role in improving the performance of polymer electrolyte membrane fuel cells (PEMFCs). Modifying the design of the GDL structure is an effective strategy for regulating the percolation process of liquid water and the supply of reaction gas. In this study, several GDLs with in-plane nonuniformly distributed pore sizes were designed to construct an ordered liquid water transport pathway. Two pore-size patterns with a “V” shape and an inverted “V” shape were designed through the orientation control of fiber distribution. In the inverted V-shaped pattern, the pore size exhibited a wave crest distribution along the in-plane direction, whereas, in the V-shaped pattern structure, the pore size was troughed along the in-plane direction. The three-dimensional (3D) multiphase Lattice Boltzmann method (LBM) and 3D diffusion LBM were used to investigate the liquid water percolation process and the reaction gas transport process in the GDL, respectively. The numerical results indicated that liquid water tends to concentrate in layers with macropores in the nonuniform GDL. Compared with the uniformly distributed GDL, these two pore size patterns can accelerate the drainage velocity and lower the water content. The reversed V-shaped pattern was further optimized to obtain the optimal width of the layers with macrospores. The results showed that a length of 96 μm is recommended to balance the concentrated effect and low-concentration areas. Under dry conditions, the gas transport capacity was insensitive to pore size distribution, whereas, under partially saturated conditions, both the V-shaped and inverted V-shaped structures of a nonuniform design weakened the impeding effect of liquid water on the gas supply. Moreover, the effective gas diffusion coefficient of the nonuniform study can reach up to 3.85 times of the uniform structure. This work promotes the understanding of different in-plane distributed pore size styles on the water percolation behavior in the GDL, thereby contributing to the optimal design of the GDL and PEMFCs.

Development and evaluation of antibacterial nanofiber membranes via coaxial electrospinning for enhanced air filtration performance

As industrialization intensifies and the population soars, the challenge of air pollution escalates into a pressing concern. Electrospun nanofiber membranes, owing to their distinctive attributes including high specific surface area, porosity, and uniform pore size distribution, have emerged as promising candidates for air filtration. In this study, we successfully prepared ZnO@polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) antibacterial nanofiber membranes through a combined solvothermal and coaxial electrospinning approach. The structure and performance of these nanofiber membranes were systematically modulated by adjusting the shell feeding rate and zinc acetate dihydrate (Zn(Ac)2·2H2O) concentration. Specifically, an increase in the shell feeding rate led to a decrease in fiber diameter, accompanied by the proliferation of nano-beads, thereby contributing to a reduction in membrane pore size. Consequently, a heightened shell feeding rate correlated positively with both filtration efficiency and pressure drop. Furthermore, the incompletely reacted Zn(Ac)2·2H2O enhanced the conductivity of the spinning solution, facilitating a decrease in pore size and enhancing air filtration performance. In summary, when the shell feeding rate was 0.60 mL h−1 and Zn(Ac)2·2H2O concentration was 1.5 wt%, the obtained ZnO@PVDF-HFP nanofiber membrane exhibited superior air filtration performance, with high filtration efficiency of 99.91 %, low pressure drop of 80.70 Pa and noteworthy quality factor of 0.08781 Pa-1. Notably, these membranes sustained their high filtration efficiency and low pressure drop even after 40 min of continuous testing, underscoring their exceptional stability. In addition, the obtained nanofiber membrane exhibited robust antibacterial activity against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), demonstrating their multifaceted potential. Our work not only simplifies the fabrication process of electrospun nanofiber membranes with superior air filtration and antibacterial properties but also highlights their potential as innovative alternatives to conventional air filter materials, poised for diverse practical applications.

Concentrating Cocoa Polyphenols-Clarification of an Aqueous Cocoa Extract by Protein Precipitation and Filtration.

The seeds of Theobroma cacao L. are rich in antioxidant flavonoids such as flavan-3-ols, which are valued for their health benefits. In this context, it is of interest to improve flavanol content in cocoa extracts. The present study aimed at improving the clarification process of an aqueous cocoa extract using protein precipitation and filtration. Five pH modifications and two bentonite amounts were tested for their effects on protein precipitation and flavanol content. Micro- and ultrafiltration as a subsequent step was done by testing three different ceramic membranes (30, 80, and 200 nm). Lower pH in pre-treatment reduced protein content and kept flavanols constant, while at higher pH, flavanols were reduced up to 40%. Larger membrane pores enhanced polyphenol permeation, while smaller pores limited protein permeation. Adjusting pH to the isoelectric point increased protein adsorption, improving filtration quality despite decreased permeate flux. However, membrane fouling results in higher permeate quality due to increased selectivity. Furthermore, the addition of bentonite during filtration reduced both protein and flavanol content in the permeate, similar to the effects seen in the pre-treatment of the supernatant. Optimizing pH and membrane pore size enhances the recovery and quality of polyphenols during filtration, balancing protein removal and flavanol retention.

Hydrogen bond-mediated assembly of homo-charged COF nanosheets and polyelectrolytes towards robust Li+/Mg2+ separation membrane

Developing membranes with ordered channels and high positive charge density is crucial for Li+/Mg2+ separation. Ionic covalent organic framework (COF) membranes are promising candidates, yet they face challenges like pore size mismatch with ions and the liable structural defects. Herein, we proposed a hydrogen bond-mediated strategy to assemble membranes from homo-charged COF nanosheets and polyelectrolytes. Compared with the quaternary amines in poly (diallyl dimethyl ammonium chloride), the abundant primary and secondary amines in polyethyleneimine facilitate multiple hydrogen bonding interactions with COF nanosheets. These interactions effectively overcome the electrostatic repulsion between positive charges, endowing membrane with structural robustness. Furthermore, the intercalation of polyelectrolytes eliminates the structural defects, reduces the membrane pore size, and enhances the Donnan effect. The optimized COF membrane exhibited a pure water flux of 10.2 L m−2 h−1 bar−1, separation factor of up to 30 at high Mg2+/Li+ mass ratio of 100, and excellent stability under various operating conditions. Strikingly, our strategy facilitates the fabrication of membranes in large area (>450 cm2) while maintaining consistent separation performance, showcasing substantial potential of scalable manufacturing.

Fouling behavior heterogeneity of typical nanoplastics in widely used polyvinylidene fluoride ultrafiltration membranes

The similarity between the particle size of nanoplastics (NPs) and the pore size of membranes used in water treatment plants may cause overlooked NPs to become potential bothers of membrane processes. Also, various NPs may impact membrane processes differently. Here, fouling behaviors of typical polyvinylidene fluoride ultrafiltration membranes induced by two typical NPs were investigated in environmentally relevant conditions. Results manifested adverse effects of diverse NPs on membranes differed. The flux descent rates of diverse NPs feed solutions-fouled membranes ranged from 9 % to 36 % over 2 h at 0.10 MPa in the dead-end filtration system. Polystyrene nanoplastics caused severer membrane fouling and greater cleaning difficulty than polyethylene nanoplastics did, and the fouling and the cleaning difficulty were both exacerbated with divalent cations present. Also, the incipient fouling was the chief driver. The obtained fouling behavior and cleaning efficiency were compared to the interaction energy data calculated by DLVO theory to better understand underlying fouling mechanisms. Significant correlations were observed between them. Overall, our findings demonstrated the negative impact and its heterogeneity of different NPs on membrane processes, elucidated their mechanisms, and provided scientific bases for NPs membrane fouling control.

Fabrication and assessment of performance of clay based ceramic membranes impregnated with CNTs in dye removal

In this research, flat disk clay-based ceramic membranes were fabricated and optimized for use in the treatment of wastewater contaminated with dye. The properties of the fabricated membranes were assessed to optimize the fabrication conditions, namely, the firing temperature (1150 °C, 1200 °C, and 1250 °C), soaking time (30 min and 60 min) and zeolite percentage (0%, 10%, and 20%). On the other hand, the rejection of methylene blue dye (MB) and acid fuchsin dye (AF) was studied. The surface of the optimal membrane support was modified using functionalized COOH-carbon nanotubes to increase the dye removal percentage. The fabricated membranes were characterized using FTIR, XRD, and XRF. The optimum membrane support was fabricated at 1150 °C, after 30 min of soaking and with 0% zeolite. The most suitable membrane support was found to be AF, as its rejection percentages reached 42% and 95% without and after surface modification, respectively. The surface of the membrane was examined via SEM, which revealed normally distributed pores. The average pore size of the final membrane was found to be 0.076 micrometers using a mercury porosimeter; thus, the produced membranes can be used in ultrafiltration applications. Finally, the fouling properties showed that the total fouling reached 72.8%, of which only 2.1% was irreversible.

Effect of Membrane Pore Size on Copper Recycling from Waste Printed Circuit Boards by Slurry Electrolysis

Effect of Membrane Pore Size on Copper Recycling from Waste Printed Circuit Boards by Slurry Electrolysis

Tailor-Made Heterocharged Covalent Organic Framework Membrane for Efficient Ion Separation.

Pore size sieving, Donnan exclusion, and their combined effects seriously affect ion separation of membrane processes. However, traditional polymer-based membranes face some challenges in precisely controlling both charge distribution and pore size on the membrane surface, which hinders the ion separation performance, such as heavy metal ion removal. Herein, the heterocharged covalent organic framework (COF) membrane is reported by assembling two kinds of ionic COF nanosheets with opposite charges and different pore sizes. By manipulating the stacking quantity and sequence of two kinds of nanosheets, the impact of membrane surface charge and pore size on the separation performance of monovalent and multivalent ions is investigated. For the separation of anions, the effect of pore size sieving is dominant, while for the separation of cations, the effect of Donnan exclusion is dominant. The heterocharged TpEBr/TpPa-SO3H membrane with a positively charged upper layer and a negatively charged bottom layer exhibits excellent rejection of multivalent anions and cations (Ni2+, Cd2+, Cr2+, CrO4 2-, SeO3 2-, etc). The strategy provides not only high-performance COF membranes for ion separation but also an inspiration for the engineering of heterocharged membranes.